1. Field of the Invention
The invention relates to a position detecting device for finding the distance between a specimen arranged in a conductive structure and a microwave antenna arrangement of the position detecting device on the basis of microwaves and to a method for the manufacture of a position detecting device.
2. Description of the Related Art
Such a position detecting device is for example described in the German patent publication DE 102 05 904 A1. The conductive structure is constituted by a housing of a pneumatic cylinder or of a hydraulic cylinder, in which a piston is arranged for longitudinal motion. The position detecting device serves for finding the distance of the piston with respect to a longitudinal terminal position, in the vicinity of which the microwave antenna arrangement is arranged. The microwave antenna arrangement comprises a coupling probe, which is held by a dielectric holding system. The housing or, respectively, the conductive structure cooperate with the coupling probe as regards the propagation of the microwaves. It is essential for the distance of the coupling probe from the housing be constant, that is to say that the dielectric holding system ensures having this constant distance.
Accordingly the manufacture of the position detecting device or, respectively, of the cylinder with the position detecting device is impeded and made more expensive, since low manufacture tolerances must be adhered to. Furthermore during the operation of the cylinder or, respectively, of the position detecting device the relative distance of the coupling probe from the conductive structure, that is to say from the housing of the cylinder, may vary, for example owing to pressure loads, mechanical vibrations or the impact of the piston against a terminal abutment in the microwave antenna arrangement.